Retrieve and parse --print=check-cfg in RustcTargetData

Author: Urgau

src/cargo/core/compiler/build_context/target_info.rs

@@ -944,6 +944,9 @@ pub struct RustcTargetData<'gctx> {
     target_config: HashMap<CompileTarget, TargetConfig>,
     /// Information about the target platform that we're building for.
     target_info: HashMap<CompileTarget, TargetInfo>,
+
+    /// `--print=cfg`
+    check_cfg: CheckCfg,
 }
 
 impl<'gctx> RustcTargetData<'gctx> {
@@ -990,6 +993,35 @@ impl<'gctx> RustcTargetData<'gctx> {
             }
         };
 
+        let check_cfg = {
+            let mut process = rustc.workspace_process();
+
+            apply_env_config(gctx, &mut process)?;
+            process
+                .arg("-")
+                .arg("--print=check-cfg")
+                .arg("--check-cfg=cfg()")
+                .arg("-Zunstable-options")
+                .env_remove("RUSTC_LOG");
+
+            // Removes `FD_CLOEXEC` set by `jobserver::Client` to pass jobserver
+            // as environment variables specify.
+            if let Some(client) = gctx.jobserver_from_env() {
+                process.inherit_jobserver(client);
+            }
+
+            let (output, _error) = rustc
+                .cached_output(&process, 0)
+                .with_context(|| "failed to run `rustc` to learn about check-cfg information")?;
+
+            let lines = output.lines();
+
+            lines.fold(CheckCfg::default(), |mut check_cfg, line| {
+                check_cfg.process_line(line);
+                check_cfg
+            })
+        };
+
         let mut res = RustcTargetData {
             rustc,
             gctx,
@@ -998,6 +1030,7 @@ impl<'gctx> RustcTargetData<'gctx> {
             host_info,
             target_config,
             target_info,
+            check_cfg,
         };
 
         // Get all kinds we currently know about.
@@ -1074,6 +1107,11 @@ impl<'gctx> RustcTargetData<'gctx> {
         self.info(kind).cfg()
     }
 
+    /// Gets the list of check-cfg
+    pub fn check_cfg(&self) -> &CheckCfg {
+        &self.check_cfg
+    }
+
     /// Information about the given target platform, learned by querying rustc.
     ///
     /// # Panics